> Residual current devices. Operating principle. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Residual current devices. The principle of operation of the RCD. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Current Devices

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The conductors passing through the window of the magnetic circuit form the oppositely connected primary windings of the differential current transformer.

If we denote the current flowing towards the load as I₁ and from the load - as I₂, then we can write the equality

I₁ = I_2.

Equal currents in oppositely connected windings induce equal, but vectorially oppositely directed magnetic fluxes in the magnetic core of the current transformer₁ and F₂. The resulting magnetic flux is zero, the current in the secondary winding of the differential transformer is also zero.

The starting body is in this case at rest. When a person touches open conductive parts or the body of the electrical receiver, on which the insulation breakdown occurred, along the phase conductor through the RCD, except for the load current I₁ additional current flows - leakage current I_ut, which is differential (difference) for the current transformer - I_Δ. In this case I_ut = I_Δ.

The inequality of currents in the primary windings (I₁₊I_Δ) in the phase conductor and I₂, equal to I₁ in the zero working conductor cause an imbalance of magnetic fluxes and, as a result, the occurrence of a transformed differential current in the secondary winding.

The principle of operation of the RCD is explained by the diagram shown in Fig. 14.15. If this current exceeds the setting value of the threshold element of the trigger element 2, the latter operates and acts on the actuator 3.

Rice. 14.15. The principle of operation of the RCD: 1 - differential current transformer; 2 - threshold element; 3 - actuator; 4 - circuit testing

The actuator, usually consisting of a spring drive, a release mechanism and a group of power contacts, opens the electrical circuit. As a result, the electrical installation protected by the RCD is de-energized.

To carry out periodic monitoring of the serviceability (operability) of the RCD, it is provided chain testing 4. Pressing "Test"An artificially created circuit for the flow of a tripping differential current. The operation of the RCD in this case means that the device as a whole is in good order.

Author: Koryakin-Chernyak S.L.

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